Unsharp mask filter
Tracy M.
I use the unsharp mask filter a lot, but haven't read any info
about its use. Just want to check out the tips other people
have about sharpen, unsharp mask.
What I usually do is, sharpening photos for the web:
Select the area I wish to sharpen
Choose filter, sharpen, unsharp mask
Usually set it for 100% sharpening- have never found a need to set
it above 150%
Determine the best radius - usually .3 - .8 for faces,
.8 - 1.2 for other parts of a picture. Have never needed
to use a radius above 1.5.
Leave threshold at 0. I'd like to know more about threshold, and
when it's a good idea to raise the setting. All I know about
it is that it creates a more abrupt, dramatic sharpening effect
(and I haven't found a reason to use it yet)
Also, I learned to use unsharp mask as the LAST step in fixing up
a photo, and certainly before any resizing, resampling or
changes in file format (except the final step of switching to jpg).
Sometimes...especially with faces, I do unsharp mask, look closely
at the results and find a portion of the face or body that
doesn't look good sharpened. So I do edit, undo, then lasso that
portion, do a select inverse, and reapply the unsharp mask,
leaving that area that doesn't need sharpening untouched.
Occasionally, instead, I zoom in and darken a few of the pixels
in small areas where the sharpening doesn't look good (frequently
because it creates too large a white halo around an area, or
in the case of dithered skin color, emphasizes the dithering).
Usually then, I set the eyedropper on the neighboring darker pixel and
pencil or brush to extend it outward by one pixel to undo a small
portion of the image that has too much sharpening.
(Most of my 75+ skating photos starting at
http://www.webwinds.com/skating/skating.htm were saved with unsharp,
mask. In many cases,the faces were very blurry....but I was able to
bring out the detail and enlarge the photos with relatively good
results).
I'd like to learn more tips for using this filter effectively
though, since I rely it on so much. Any other tips and exlanations
from others? TIA.....
(I find the two most useful filters for web graphics to be
gaussian blur and unsharp mask.)
Tracy
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Ross Fenmore
Tracy M. wrote:
>
> I use the unsharp mask filter a lot, but haven't read any info
> about its use. Just want to check out the tips other people
> have about sharpen, unsharp mask.
>
Here he is again. Can't get rid of me.
The Unsharp Mask filter increases contrast between neighboring pixels which makes
edges more prominent. If you make a graduated ramp of grayscale bars, you can see
how Unsharp mask affects the edges. At high settings, the edge of a lighter bar
approaches white; a darker bar approaches black. Try different radius and threshold
settings to see their affect - (it's a quick way to make paneling). Note: to create
the bars, make a linear gradient from black to white, use Image > Adjust > Posterize
to set the number of bars...
> What I usually do is, sharpening photos for the web:
>
> Select the area I wish to sharpen
> Choose filter, sharpen, unsharp mask
> Usually set it for 100% sharpening- have never found a need to set
> it above 150%
The maximum amount to use for non-special-effects is about 200%, depending on what
you're sharpening, and what the other settings are. When converting grayscale images
to bitmap mode, as much as 400% can be useful. 100% is a good place to start for
normal applications...
> Determine the best radius - usually .3 - .8 for faces,
> .8 - 1.2 for other parts of a picture. Have never needed
> to use a radius above 1.5.
The radius setting determines the amount of space around each pixel that is
affected. The effect is distributed throughout that space, so fractional values will
affect the amount of contrast produced even though there's no such thing as half a
pixel. 2.0 is about the maximum useful value for most purposes, though, as you say,
1.5 is a much more common limit.
> Leave threshold at 0. I'd like to know more about threshold, and
> when it's a good idea to raise the setting. All I know about
> it is that it creates a more abrupt, dramatic sharpening effect
> (and I haven't found a reason to use it yet)
Threshold sets the amount of difference there needs to be between two shades before
they are sharpened. For skin tones, a setting between 2-15 will keep them looking
smooth because areas of small existing contrast will be left alone. Larger values
will reduce the amount of sharpening to areas that already have sufficient contrast.
Very large values will reduce sharpening to nothing no matter what the other
settings are.
> Also, I learned to use unsharp mask as the LAST step in fixing up
> a photo, and certainly before any resizing, resampling or
> changes in file format (except the final step of switching to jpg).
>
Using Unsharp mask AFTER resampling is a standard procedure. The effect of
interpolation is to average pixels, and therefore softens or blurs edges. Use the
Type tool to make some text and then resample. The softer edges will be quite
evident. Then use Unsharp Mask and see the improvement. Images that have been
compressed with the jpeg algorithm can be poor candidates for sharpening. Artifacts
are enhanced. If you can see the blocky areas before sharpening, they'll really be
noticeable after. In fact, sometimes blurring can improve a jpeg more than
sharpening.
> Sometimes...especially with faces, I do unsharp mask, look closely
> at the results and find a portion of the face or body that
> doesn't look good sharpened. So I do edit, undo, then lasso that
> portion, do a select inverse, and reapply the unsharp mask,
> leaving that area that doesn't need sharpening untouched.
>
You could also duplicate the layer. Sharpen the duplicate, then paint out (or
select/fill) the effect on a layer mask, with variable opacity.
> Occasionally, instead, I zoom in and darken a few of the pixels
> in small areas where the sharpening doesn't look good (frequently
> because it creates too large a white halo around an area, or
> in the case of dithered skin color, emphasizes the dithering).
>
You can create two duplicates of your layer, both sharpened to the max. Put one
duplicate layer in Lighten mode, the other in Darken. Adjust opacity individually.
Lower the opacity of the Lighten layer to reduce white halos.
> Usually then, I set the eyedropper on the neighboring darker pixel and
> pencil or brush to extend it outward by one pixel to undo a small
> portion of the image that has too much sharpening.
>
> (Most of my 75+ skating photos starting at
> http://www.webwinds.com/skating/skating.htm were saved with unsharp,
> mask. In many cases,the faces were very blurry....but I was able to
> bring out the detail and enlarge the photos with relatively good
> results).
>
> I'd like to learn more tips for using this filter effectively
> though, since I rely it on so much. Any other tips and exlanations
> from others? TIA.....
>
> (I find the two most useful filters for web graphics to be
> gaussian blur and unsharp mask.)
>
> Tracy
>
I agree. I have function keys assigned to both of them for quick access.
Ross